Dart: Simplifies the handle watcher. Various cleanups and bugfixes.

mojo/public/dart/src/data_pipe.dart

Index: mojo/public/dart/src/data_pipe.dart
diff --git a/mojo/public/dart/src/data_pipe.dart b/mojo/public/dart/src/data_pipe.dart
index 665285de4a953d5b8a3287300240e5ebe31e13ce..11fc55d4c2e66537f35a4d958c91224a60f36c8a 100644
--- a/mojo/public/dart/src/data_pipe.dart
+++ b/mojo/public/dart/src/data_pipe.dart
@@ -96,14 +96,14 @@ class MojoDataPipeConsumer {
   static const int FLAG_ALL_OR_NONE = 1 << 0;
   static const int FLAG_MAY_DISCARD = 1 << 1;
   static const int FLAG_QUERY = 1 << 2;
+  static const int FLAG_PEEK = 1 << 3;
 
   RawMojoHandle handle;
   MojoResult status;
   final int element_bytes;
 
-  MojoDataPipeConsumer(this.handle,
-                       this.status,
-                       this.element_bytes);
+  MojoDataPipeConsumer(
+      this.handle, [this.status = MojoResult.OK, this.element_bytes = 1]);
 
   int read(ByteData data, [int num_bytes = -1, int flags = 0]) {
     if (handle == null) {
@@ -123,7 +123,7 @@ class MojoDataPipeConsumer {
     return result[1];
   }
 
-  ByteData beginRead(int buffer_bytes, [int flags = 0]) {
+  ByteData beginRead([int buffer_bytes = 0, int flags = 0]) {
     if (handle == null) {
       status = MojoResult.INVALID_ARGUMENT;
       return null;
@@ -150,6 +150,8 @@ class MojoDataPipeConsumer {
     status = new MojoResult(result);
     return status;
   }
+
+  int query() => read(null, 0, FLAG_QUERY);
 }